Studies will be made on the hepatic mitochondrial changes produced by glucagon treatment of rats and isolated liver cells. Because hormonal effects persist in submitochondrial particles, these particles will be used for most experiments. A working hypothesis is that glucagon treatment changes mitochondrial function by stimulating the phosphorylation of a critical protein of the organelles. The proteins of the submitochondrial particles will be separated by gel electrophoresis after labeling by incubation of liver cells with 32P. It is hoped that one or a few protein bands will show a stimulation of labeling by hormone treatment and that identification of the labeled protein will be possible. Conditions will be looked for that will allow cyclic adenylic acid to stimulate the phosphorylation of this putative target protein in isolated mitochondria.